Of the top of my head, I don't use Bishop or Zhjaeve enough to find that jackpot influence gains like I did with Elaine in Jerro's Stronghold, Khelgar at the Scout Camp when finding the lost stronghold, etc.
Are there any one spot big gains for these two characters? By my counts, they are both only about +2 or so since I got both of them --- The School of the Undefeated of the East! The winds of the king! Zenshin! Keiretsu! Tenpakyouran! Look, the East is burning red!
*spoilers* You can gain influence with Zhjaeve when you're trying to complete the Rituals and you get to the door that damages you when you try to open it. Just keep trying until it runs out of steam and Zhjaeve respects you more.
Otherwise, you get more through dialogue. You can also get some influence with her if you choose her to help you defend the Keep.
Bishop is a little easier, however there's not really any 'big' place to gain influence. You can gain some from the Gith prison, one by snapping the Zeeaire's neck. You can also gain some through dialogue with him as well as taking him to meet the ranger in Port Llast and insulting her.
However, most Bishop influence gains actually detract influence from others. In fact, all of them do for Casavir, some from Shandra, and so on.
There's a site, Thieves Guild.net, or something, that has also the influence changes in it, act by act. Check it out. --- I wish for this night-time to last for a life-time